The role played by catecholamines in the control of the secretion of prolactin will be investigated. It is visualized that the activation of the hypothalamic adrenergic system results in increased secretion of dopamine into hypophysia portal blood. Dopamine is carried by the blood to the anterior pituitary gland where it inhibits the secretion of prolactin, but not that of other pituitary hormones. Another proposed route is that dopamine reaches the anterior pituitary gland from the posterior pituitary where it is stored after being transported down from the hypothalamus via nerve tracts. The dynamics of catecholamine activation in relation to the secretion of prolactin will be investigated by using the techniqes of hypophysial portal collection from anesthetized rats, and jugular blood collection from conscious rats. The possible role of the posterior pituitary in the regulation of prolactin release will be investigated by using the method of posterior lobectomy. Plasma prolactin, LH and FSH will be determined by radioimmunoassays whereas tissue and plasma dopamine, norepinephrine and epinephrine will be simultaneously determined by a sensitive double isotope radioenzymatic assay. The second major study to be pursued will focus on the demonstration that PIF (prolctin inhibiting factor) activity in the hypothalamus, posterior pituitary and hypophysial portal blood is attributable to dopamine. This will be done by utilizing several purification and chromatographic techniques, followed by the detection of PIF activity by a pituitary superfusion and incubation systems. A correlation will be made between changes in PIF activity and changes in endogenous catecholamine concentration.